1. Field of the Invention
This invention relates generally to processing of radio-frequency transmitted data and, more particularly, to processing of real-time data transmitted between fixed ground stations and as mobile aircraft as part of an aircraft combat training system.
2. Description of the Related Art
Military training of aircraft combat crews involves maneuvering aircraft across specified terrain and airspace in simulated battle operations. Instrumentation mounted in the aircraft provides position information and performance data to ground-based stations, which collect the aircraft data, process it, and generate reports on likely combat effectiveness of the crews and equipment. A wide variety of aircraft operations can be simulated, including air combat and ground attack. The data processing can determine the likely effect of weapons delivery, keep track of objects being fired upon, and assess likely damage to targets and to attacking aircraft.
The instrumentation is generally carried by aircraft in pods mounted at aircraft weapons stations, and is referred to as Air Combat Maneuvering Instrumentation (ACMI). One well-known instrumentation specification and data protocol, used by the armed forces of the U.S.A., is referred to as Tactical Air Combat Training System (TACTS). Data in TACTS is transmitted at the rate of either approximately 62 kilobits per second (KBPS) or 198.4 KBPS. The TACTS data includes aircraft identification and operational data such as weapons load and remaining fuel. The digital data is modulated and mixed with a carrier frequency for transmission over the radio frequency (RF) band.
The TACTS data transmitted by an aircraft permits aircraft position to be derived by a process known as multilateral triangulation. In multilateral triangulation, an aircraft receives data from a ground station and transmits data to multiple ground stations. The range (straight-line distance) from the aircraft to any one of the ground stations is determined by measuring the phase of a sinusoidal signal modulated onto a carrier frequency received and re-transmitted by the aircraft. Range data from any three ground stations will determine the aircraft position in terms of latitude, longitude, and altitude.
The speed of the aircraft involved in ACMI systems can vary greatly, from zero (hovering speeds) in the case of helicopters to hundreds of miles per hour in the case of supersonic aircraft. The ACMI ranges cover many square miles of land and the altitudes involved can vary from ground level to tens of thousands of feet. All of the data must be transmitted, received, collected, and processed in real time. This presents a very demanding signal processing task to ensure accuracy and reliability. The TACTS specification has been in use since approximately the 1970s.
A system having greater data transmission capability has been proposed for use at the military range located at Nellis Air Force Base, Nevada, U.S.A. The new system is called Nellis Air Combat Training System (NACTS) and specifies data transmission at the rate of 1.44 megabits per second (MBPS), or 1440 KBPS. Because of the advent of systems such as the Global Positioning Satellite (GPS) system, the NACTS protocol does not rely on multilateral triangulation for determining aircraft position. As with the TACTS implementation, the NACTS data is transmitted from pods attached to aircraft and relayed to ground stations, where the data is processed. The increased data rate of NACTS can support, for example, an increased number of aircraft participating in any training exercise or an increased amount of data transmitted for each aircraft.
As noted above, the TACTS specification has been in use for many years. Many training facilities have used, and will continue to use, the TACTS specification. Thus, it would be advantageous if an ACMI pod for use with training systems could support both the TACTS and NACTS specifications. A characteristic of continuing importance is the accurate detection of received data and, in particular, the identification of data pulses. Efficient construction and operation, in the form of low weight and low power requirements, also is important so as to minimally impact aircraft operation.
From the discussion above, it should be apparent that there is a need for a processing system that can operate with multiple data protocol specifications, waveforms, and data rates, while ensuring accurate and reliable detection of data streams in an aircraft operational environment. The present invention fulfills this need.